Micro-electro-mechanical system (mems) variable capacitor apparatuses and related methods

ABSTRACT

Systems, devices, and methods for micro-electro-mechanical system (MEMS) tunable capacitors can include a fixed actuation electrode attached to a substrate, a fixed capacitive electrode attached to the substrate, and a movable component positioned above the substrate and movable with respect to the fixed actuation electrode and the fixed capacitive electrode. The movable component can include a movable actuation electrode positioned above the fixed actuation electrode and a movable capacitive electrode positioned above the fixed capacitive electrode. At least a portion of the movable capacitive electrode can be spaced apart from the fixed capacitive electrode by a first gap, and the movable actuation electrode can be spaced apart from the fixed actuation electrode by a second gap that is larger than the first gap.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to co-pending U.S. patent applicationSer. No. 16/511,899, filed Jul. 15, 2019, which is a continuation ofissued U.S. patent application Ser. No. 14/033,434, filed Sep. 20, 2013,which claimed priority to U.S. Provisional Patent Application Ser. No.61/703,595, filed Sep. 20, 2012, the disclosures of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The subject matter disclosed herein relates generally tomicro-electro-mechanical system (MEMS) devices and methods for thefabrication thereof.

More particularly, the subject matter disclosed herein relates tosystems, devices, and methods for MEMS variable capacitors.

BACKGROUND

Micro-electro-mechanical systems (MEMS) can be used to create variablecapacitors. Specifically, for example, as shown in FIG. 1a , a variablecapacitor 1 can include a substrate 10 on which one or more fixedactuation electrodes 11 and one or more fixed capacitive electrodes 12can be positioned. A movable component 20 can be suspended abovesubstrate 10, movable component 20 being fixed with respect to substrate10 at either end. Movable component 20 can include one or more movableactuation electrodes 21 and one or more movable capacitive electrodes22. In this configuration, by controlling a potential difference betweenfixed actuation electrodes 11 and movable actuation electrodes 21,movable component 20 can be selectively moved toward or away fromsubstrate 10. In this way, the capacitance between fixed capacitiveelectrode 12 and movable capacitive electrode 22 can be selectivelyvaried. In some aspects, a layer of dielectric material can be depositedto cover the actuation electrode 11 and capacitive electrode 12. Thedielectric material can be planarized to provide a flat surface.

In some aspects, the substrate 10 and moveable component can be fixed bytwo anchor or support structures 23 on both ends as illustrated in FIG.1B. In such configuration, however, applying a potential differencebetween fixed actuation electrodes 11 and movable actuation electrodes21 can cause movable component 20 to flex toward substrate 10 unevenly,which can cause issues with charging in the actuator dielectric andwear. Furthermore, although it is desirable for movable capacitiveelectrode 22 to be able to move fully downward so that it can contactfixed capacitive electrode 12 to maximize the capacitance range, it canbe undesirable for fixed actuation electrodes 11 and movable actuationelectrodes 21 to get too close to one another since the electrodes canbe subject to suddenly “snapping down” together after moving closeenough to one another, as illustrated in FIG. 1B, and the device cansuffer from dielectric damages and stiction caused by high electricfields between the actuator electrode for spacings that are too close.

Accordingly, it would be desirable for systems, devices, and methods forMEMS variable capacitors to more consistently bring its capacitorelectrodes into close proximity while maintaining sufficient spacing ofthe adjacent actuator(s).

SUMMARY

In accordance with this disclosure, systems, devices, and methods formicro-electro-mechanical system (MEMS) tunable capacitors are provided.In one aspect, a MEMS variable capacitor is provided having a fixedactuation electrode attached to a substrate, a fixed capacitiveelectrode attached to the substrate, and a movable component positionedabove the substrate and movable with respect to the fixed actuationelectrode and the fixed capacitive electrode. The movable component caninclude a movable actuation electrode positioned above the fixedactuation electrode and a movable capacitive electrode positioned abovethe fixed capacitive electrode. At least a portion of the movablecapacitive electrode can be spaced apart from the fixed capacitiveelectrode by a first gap, and the movable actuation electrode can bespaced apart from the fixed actuation electrode by a second gap that islarger than the first gap.

In some aspects, a MEMS variable capacitor can include a fixedcapacitive electrode attached to a substrate, a first fixed actuationelectrode and a second fixed actuation electrode attached to thesubstrate on opposing sides of the fixed capacitive electrode, and amovable component comprising a first end that can be fixed with respectto the substrate and a second end opposite the first end that can befixed with respect to the substrate, a center portion of the movablecomponent being positioned above the substrate and movable with respectto the fixed capacitive electrode, the first fixed actuation electrode,and the second fixed actuation electrode. The movable component caninclude a first movable actuation electrode positioned above the firstfixed actuation electrode, a second movable actuation electrodepositioned above the second fixed actuation electrode, and a movablecapacitive electrode positioned above the fixed capacitive electrode. Atleast a portion of the movable capacitive electrode can be spaced apartfrom the fixed capacitive electrode by a first gap, and wherein thefirst movable actuation electrode and the second movable actuationelectrode can be spaced apart from the first fixed actuation electrodeand the second fixed actuation electrode, respectively, by a second gapthat is larger than the first gap.

In another aspect, a method for manufacturing a MEMS variable capacitoris provided. The method can include depositing a fixed actuationelectrode on a substrate, depositing a fixed capacitive electrode on thesubstrate, depositing a sacrificial layer over the fixed actuationelectrode and the fixed capacitive electrode, etching the sacrificiallayer to form a recess in a region of the sacrificial layer above thefixed capacitive electrode, depositing a movable actuation electrode onthe sacrificial layer above the fixed actuation electrode, depositing amovable capacitive electrode in the recess of the sacrificial layerabove the fixed capacitive electrode, depositing a structural materiallayer on the movable actuation electrode and the movable capacitiveelectrode, and removing the sacrificial layer such that the movableactuation electrode, the movable capacitive electrode, and thestructural material layer define a movable component suspended above thesubstrate and movable with respect to the fixed actuation electrode andthe fixed capacitive electrode. At least a portion of the movablecapacitive electrode can be spaced apart from the fixed capacitiveelectrode by a first gap, and the movable actuation electrode can bespaced apart from the fixed actuation electrode by a second gap that islarger than the first gap.

In yet another aspect, a micro-electro-mechanical system (MEMS) variablecapacitor can include a fixed actuation electrode attached to asubstrate, a fixed capacitive electrode attached to the substrate, and amovable component positioned above the substrate and movable withrespect to the fixed actuation electrode and the fixed capacitiveelectrode. The movable component can include a movable actuationelectrode positioned above the fixed actuation electrode, a movablecapacitive electrode positioned above the fixed capacitive electrode,and at least one standoff bump attached to the movable component at ornear the movable actuation electrode. Where at least a portion of themovable capacitive electrode can be spaced apart from the fixedcapacitive electrode by a first gap. Furthermore, the movable actuationelectrode can be spaced apart from the fixed actuation electrode by asecond gap that is larger than the first gap, and the at least onestandoff bump can protrude from the movable actuation electrode adistance that is substantially equal to the difference between thedimensions of the first gap and the second gap.

Although some of the aspects of the subject matter disclosed herein havebeen stated hereinabove, and which are achieved in whole or in part bythe presently disclosed subject matter, other aspects will becomeevident as the description proceeds when taken in connection with theaccompanying drawings as best described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present subject matter will be morereadily understood from the following detailed description which shouldbe read in conjunction with the accompanying drawings that are givenmerely by way of explanatory and non-limiting example, and in which:

FIGS. 1A through 1D are side views of conventional variable capacitorconfigurations;

FIGS. 2A through 2H are side views of variable capacitor configurationsaccording to various embodiments of the presently disclosed subjectmatter;

FIGS. 3A through 3H are side views of various variable capacitorconfigurations according to an embodiment of the presently disclosedsubject matter;

FIGS. 4A through 4D are side views of various variable capacitorconfiguration according to an embodiment of the presently disclosedsubject matter;

FIGS. 5A to 5E are cross sectional views of standoff bumps located inmovable actuation regions of a MEMS device according to an embodiment ofthe presently disclosed subject matter; and

FIGS. 5F and 5G are side views illustrating standoff bumps as they areplaced in movable actuation regions of a MEMS device according to anembodiment of the presently disclosed subject matter.

DETAILED DESCRIPTION

The present subject matter provides systems, devices, and methods forMEMS variable capacitors. In one aspect, the present subject matterprovides configurations for MEMS variable capacitors that exhibitimproved cycling lifetimes, allow improved capacitor contact, enable asnap pull-in characteristic that can be desirable for stable two-stateoperation, and reduce actuator stiction, contact forces, charging,breakdown, cycling, and/or hold down. To achieve these benefits, a MEMSvariable capacitor can be configured to have different gap distancesbetween the capacitor electrodes compared to the actuator electrodes. Insuch a configuration, the capacitor electrodes can be brought togetherwhile maintaining the actuator electrodes at desirable distances apart.

In some aspects, as illustrated in FIG. 1C, the movable component 20 canhave additional actuation 21 and/or capacitive 22 electrodes on its topsurface. This may form a mechanical structure that is balanced in stressand over temperature leading to a stable beam shape in fabrication andin operation. Electrical current can be connected to the electrodeslocated on the top surface and this can contribute to lower resistivelosses and a more robust movable component 20 under high currentconditions. In some other aspects, the entire movable component 20 canbe made out of metal, as illustrated in FIG. 1D. According to thisparticular setup, a shunt capacitor can be constructed by coupling theactuation electrodes 11 and capacitive electrode 12 to a groundedmoveable component 20.

Furthermore, FIGS. 2A through 2H illustrate a variety of variablecapacitor configuration that each decouple the dimensions of the airgaps between the capacitor plates and the actuator plates. As shown inFIG. 2a , for instance, for a variable capacitor, generally designated100, a substrate 110 can include one or more fixed actuation electrodes111 and at least one fixed capacitive electrode 112 positioned thereon.A movable component 120 can be suspended above substrate 110 and includeone or more movable actuation electrodes 121 and at least one movablecapacitive electrode 122. Movable component 120 can comprise a first endthat is fixed with respect to substrate 110 and a second end oppositethe first end that is fixed with respect to substrate 110. In this way,movable capacitive electrode 122 can be movable in a directionsubstantially perpendicular to a surface of substrate 110 to which fixedcapacitive electrode 112 is attached.

Rather than fixed actuation electrodes 111 and fixed capacitiveelectrode 112 being arranged coplanar as in FIG. 1D, fixed capacitiveelectrode 112 can be raised above the surface of substrate 110 relativeto fixed actuation electrodes 111). To accomplish this offset, aninsulating pedestal 115 (e.g., an oxide material layer) is provided onsubstrate 110 prior to fixed capacitive electrode 112 being positionedover substrate 110. In some other aspects, this can be accomplished bydepositing metal over the pedestal 115 and patterning the metal layer.In this configuration, movable capacitive electrode 122 is spaced apartfrom fixed capacitive electrode 112 by a first gap, and movableactuation electrodes 121 are spaced apart from fixed actuationelectrodes 111 by a second gap that is larger than the first gap. Inthis way, movable capacitive electrode 122 can be moved into closeproximity with fixed capacitive electrode 112 while maintaining adesired distance between movable actuation electrodes 121 and fixedactuation electrodes 111.

Similarly, in an alternative configuration shown in FIG. 2b , forexample, a protrusion 125 can be provided between movable component 120and movable capacitive electrode 122. In this way, movable capacitiveelectrode 122 can be offset toward fixed capacitive electrode 112 withrespect to movable actuation electrodes 121.

In yet a further alternative configuration shown in FIG. 2c , forexample, movable actuation electrodes 121 can be at least partiallyembedded in movable component 120. For example, in a process formanufacturing variable capacitor 100, fixed actuation electrodes 111 andfixed capacitive electrodes 112 can be deposited or otherwise attachedto substrate 110. A sacrificial layer can be provided over fixedactuation electrodes 111 and fixed capacitive electrode 112, and thesacrificial layer can be etched to form a recess in a region of thesacrificial layer above fixed capacitive electrode 111. Movableactuation electrodes 121 can be provided on the sacrificial layer abovefixed actuation electrodes 111, and movable capacitive electrode 122 canbe provided in the recess of the sacrificial layer above fixedcapacitive electrode 112. Movable component 120 can be formed byproviding a structural material layer on movable actuation electrodes121 and movable capacitive electrode 122. The sacrificial layer can beremoved such that movable actuation electrodes 121, movable capacitiveelectrode 122, and the structural material layer define movablecomponent 120 suspended above substrate 110 and movable with respect tofixed actuation electrodes 111 and fixed capacitive electrode 112.

In still a further alternative configuration shown in FIG. 2d , forexample, fixed actuation electrodes 111 can be at least partiallyembedded in substrate 110. In addition, although FIGS. 2a through 2deach only show one mechanism by which the first gap between movablecapacitive electrode 122 and fixed capacitive electrode 112 is reducedrelative to the second gap between movable actuation electrodes 121 andfixed actuation electrodes 111, those having skill in the art shouldrecognize that the different ways of offsetting the capacitiveelectrodes with respect to the actuation electrodes can be combined inany of a variety of ways to further define the differentiation in gapsizes.

In some aspects, the fixed capacitive electrode 112 can be made thickerthan the fixed actuation electrodes 111, as illustrated in FIG. 2E. Inthis way, movable capacitive electrode 122 can be offset toward fixedcapacitive electrode 112 with respect to movable actuation electrodes121. In some aspects, the movable capacitive electrode 122 can be placedcloser or further to the fixed capacitive electrode 112 depending on thedeposition depth of the electrode metal and the depth of the recessetched on the movable component 120. For example, FIG. 2C illustrates asetup where the depth of the recess is equal to the depth of the metaldeposited. Otherwise, as illustrated in FIG. 2F, the depth of the recesscan be deeper than the depth of the metal deposited, and the movablecapacitive electrode 122 can be placed closer to the fixed capacitiveelectrode 112. The thickness of the electrode 112 can be taller than orequal to the thickness of the electrodes 111. Similarly, as illustratedin FIG. 2G, sometimes the depth of the recess can be shallower than thedepth of the deposited metal, and the movable capacitive electrode 122can appear to be semi-embedded into the movable component 120, andplaced further away from the fixed capacitive electrode 112.

Alternatively, movable actuation electrodes 121 and capacitiveelectrodes 122 can all be deposited on top a sacrificial layer,resulting in the movable electrodes being embedded in the movablecomponent 120 as illustrated in FIG. 2H. in addition, fixed actuationelectrodes 111 can be embedded in the substrate 110 via a, for example,etch and metal deposition sequence. As such, a larger gap can be createdbetween the fixed actuation electrodes 111 and movable actuationelectrodes 121.

In addition to configuring the relative gap sizes, variable capacitor100 can further include additional features that can help to improvecycling lifetimes, improve capacitor contact, enable a snap pull-incharacteristic, and reduce actuator stiction, contact forces, charging,breakdown, cycling, and/or hold down. In particular, for example, asshown in FIGS. 3a and 3b , a thin dielectric layer 113 can be providedover fixed actuation electrodes 111 and fixed capacitive electrode 112to help reduce contact forces between the elements in the “closed”state, to prevent shorting of the capacitor and to provide a more stablecapacitance. In addition, at least one standoff bump 130 can be attachedto movable component 120 at or near movable actuation electrodes 121. Atleast one standoff bump 130 can protrude from movable actuationelectrodes 121 towards fixed actuation electrodes 111 for furtherpreventing contact of movable actuation electrodes 121 with fixedactuation electrodes 111. In particular, for example, at least onestandoff bump 130 can protrude from movable actuation electrodes 121 adistance that is substantially equal to the difference between thedimensions of the first gap and the second gap. Specifically, where thedistance between fixed capacitive electrode 112 and movable capacitiveelectrode 122 when in an “open” state can be defined by a gap having afirst dimension a, and the distance between fixed actuation electrodes111 and movable actuation electrodes 121 when in the “open” state can bedefined by a gap having a second dimension b that is larger than firstdimension a, at least one standoff bump 130 can protrude from movableactuation electrodes 121 a distance equal to second dimension b minusfirst dimension a. In this arrangement, when movable component 120 ismoved toward substrate 110 such that movable capacitive electrode 122contacts fixed capacitive electrode 112, at least one standoff bump 130can likewise contact fixed actuation electrodes 111, which can help tosupport movable component 120 above substrate 110 and minimize stressrelated to the attraction between fixed actuation electrodes 111 andmovable actuation electrodes 121. Furthermore, gaps 123 can be formeddue to the height difference between b and a. Such gaps 123 can improvedevice reliability by reducing actuator electric field under highvoltage conditions, and the gap width can be designed to avoidsignificantly reducing self-actuation voltage.

Furthermore, a dielectric layer 114 can be deposited on the movablecomponent 120 as shown in FIGS. 3C and 3D. In this setup, fixedactuation electrode 111 and fixed capacitive electrode 112 can bedeposited directly on top of the substrate 110 to reduce the gap spacebetween the fixed and movable electrodes. In addition, a dielectriclayer 113 can be deposited on top of the fixed electrodes 111, 112 inconformity to the existing surface topography. As such, standoff bumps130 can be shorter in height yet gap spaces 123 can still be formedbetween the movable component 120 and the substrate 110, resulting inimproved device reliability under high electric field conditions.

While FIGS. 3C-3F show dielectric layers on both movable beam and fixedelectrodes, it is understood that the dielectric layer may be on eitheror both surfaces.

Alternatively, standoff bumps can be placed on top of the dielectriclayer 113 and the fixed capacitive 111 and actuation 112 electrodes, asillustrated in FIG. 3E. According to another aspect shown in FIG. 3F, alayer of dielectric material 115 can be deposited before depositing thefixed capacitive electrode 112, therefore being placed at an elevatedposition compared to fixed actuation electrodes 111. As such, the gapdistance a is further reduced compared to the gap distance b, resultingin larger gap spaces 123 when the device is in a “closed” position.

In some aspects, the movable component 120 can accommodate standoffbumps with at least two different sizes, as illustrated in FIGS. 3G and3H. For example, standoff bumps 130 closer to the capacitive electrodes112 and 122 can be smaller in height (e.g., 0.2 μm) with this heightapproximately equal to the gap difference, if present, and one or moreadditional standoff bumps 131 closer to the support/anchor structures124 can be taller in height (e.g. 0.5 μm). As demonstrated in FIG. 3H,the taller additional standoff bumps 131 can limit the deflection of themovable component 120, thus improving device stability and reliability.It should be noted that those having skill in the art should recognizethat the standoff bumps can alternatively be conveniently placed on thefixed surface to achieve the same purpose.

Furthermore, at least one standoff bump 130 can be formed in a mannersubstantially similar to the formation of a protruding movablecapacitive electrode 122. Specifically, after positioning a sacrificiallayer over substrate 110, one or more recesses corresponding to each ofat least one standoff bump 130 can be formed in the sacrificial layer.It can be desirable to form at least one standoff bump 130 and therecess for the capacitor electrode using a single etch step into thesacrificial material. However, etch rates have a pattern dependence. Asa result, etching cavities for both movable capacitive electrode 122 andat least one standoff bump 130 into the sacrificial layer can produceunequal depths if their geometries are too different in some processes.To address this issue, movable capacitive electrode 122 can be providedas an array of electrode portions that are substantially similar in sizeto at least one standoff bump 130. In particular, as shown in FIGS. 4aand 4b , for example, movable capacitive electrode 122 can be providedas one or more protruding capacitive portions 122 a spaced apart fromfixed capacitive electrode 112 by the first gap (i.e., having a firstdimension a) and one or more recessed capacitive portions 122 b spacedapart from fixed capacitive electrode 112 by a distance greater than thefirst gap (e.g., spaced by a second dimension b). As shown in FIGS. 4aand 4b , protruding capacitive portions 122 a and recessed capacitiveportions 122 b can be provided in an alternating arrangement acrossmovable component 120. In this way, even though the portions arearranged at different heights with respect to fixed capacitive electrode112, all of the portions can together cover substantially the samefootprint as a single electrode. Although this configuration can lowerthe maximum capacitance density, it can also improve manufacturability.For example, patterning protruding capacitive portions 122 a each havinga size that is substantially similar to a size of at least one standoffbump 130 can enable similar pattern factors and thus a depth into thesacrificial layer that is more closely matched to at least one standoffbump 130. As a result, the manufacture of variable capacitor 100 can bemore consistent.

Alternatively, as shown in FIGS. 4C and 4D, metal thicknesses of thefixed actuation electrodes 111 and capacitive electrode 112 can betaller than their corresponding recesses, resulting in an uneven surfacetopography. As such, dielectric layer 113 deposited in conformity to thesurface topography will have dips between the electrodes as illustratedin FIGS. 4C and 4D. In addition, movable actuation electrodes 121 andmovable capacitive electrodes 122 a and 122 b can be formed from asingle etch on the sacrificial layer. This way the depth between theelectrodes can be more closely matched, resulting in a similar verticaldimension between the capacitor gap offset (b-a) and the standoff bumps130. Such device structure can be desirable because the closed capacitoris then held flat, as shown in FIG. 4D, and can also improve devicemanufacturability.

Regardless of the particular configuration of elements, a common featureof each of the configurations discussed herein above is that movablecapacitive electrode 122 is spaced apart from fixed capacitive electrode112 by a first gap, and movable actuation electrodes 121 are spacedapart from fixed actuation electrodes 111 by a second gap that is largerthan the first gap. The particular gap sizes can be specificallyselected to address any of a variety of performance criteria. Forexample, the difference between the size of the first gap (i.e., firstdimension a) and the size of the second gap (i.e., second dimension b)can be designed to be large enough to reduce the electric fieldgenerated between fixed actuator electrodes 111 and movable actuatorelectrodes 121, which can provide for high reliability. At the sametime, the difference between the gap sizes can be selected to be smallenough to avoid significantly reducing self-actuation voltage.Accordingly, the difference between the dimensions of the first gap andthe second gap measured in microns can be selected to be greater than avalue of a ratio between an actuation voltage V_(actuation) (e.g.,between about 10 and 100V) and a maximum electric field E_(max)generated between movable actuation electrodes 121 and fixed actuationelectrodes 111 (e.g., between about 100 and 1000 V/μm). Furthermore, thedifference between the dimensions of the first gap and the second gapcan be selected such that a self-actuation voltage between movableactuation electrodes 121 and fixed actuation electrodes 111 is above apredetermined threshold value. For example, the difference between thedimensions of the first gap and the second gap can be less than or equalto one quarter of the dimension of the second gap. In particularexemplary configurations, for instance, the difference between thedimensions of the first gap and the second gap can be between about 10nm and 500 nm.

FIG. 5A illustrates a cross sectional view of standoff bumps 530 locatedin the movable actuation region of a MEMS device, generally designated500. The bumps 530 can be square, round, octagonal or any general shapethat can be formed in a mask. In some aspects, the standoff bumps 530can be in contact with a dielectric layer 510, and isolated from theactuation metals 540. The standoff bumps 530 can be dielectric in nature(e.g., oxide material) and deposited into dips of a sacrificial layer. Aplanarization process can be performed to provide a even surface, andactuation metal 540 can be then deposited on top of the sacrificiallayer. The actuation metal 540 is patterned to remove it from above thestandoff bumps. The dielectric layer 510 can then be deposited betweenthe actuation metal 540 and onto the standoff bumps 530. In someaspects, the dielectric layer 540 can be a same type of material as thestandoff bumps 530 (e.g., oxide material).

FIG. 5B illustrates the MEMS device in a “closed” position, where thestandoff bumps 530 lays flat on a fixed dielectric surface 550. Thefixed dielectric surface 550 can rest on top of a substrate 520, and thegap spaces 555 between the actuation metal 540 and dielectric layer 550can reduce actuator electric field under high voltage conditions andimprove device reliability. The actuator metal 540 absent above thestandoff bumps 530 also greatly reduces the electric fields within thebumps and nearby dielectric layers.

Alternatively, recesses can be etched into the sacrificial layer, andstandoff bumps 530 can be formed by depositing dielectric material(e.g., oxide material) into the recesses, as illustrated in FIG. 5C.Additional dielectric layer 510 can be deposited on top of the standoffbumps 530 between the actuation metal. In some other aspects, actuationmetal 540 can be deposited and recesses can be etched between themetals. Standoff bumps 530 can be formed by a single deposition ofdielectric material into the recesses and between the metals, asillustrated in FIG. 5D.

In some aspects, recesses can be first etched into the sacrificiallayer, and a layer of dielectric material 560 can be deposited to coverthe entire surface including the recesses. Actuation metal 540 can bedeposited between the recesses, followed by a deposition of dielectricmaterial layer 510 between the metals 540, as illustrated in FIG. 5E

FIGS. 5F and 5G are side views illustrating of standoff bumps 530 in theactuation electrode region as they are placed on the bottom surface ofthe movable component of the MEMS device 500 Standoff bumps 530 can besquare, round, octagonal or any general shape that can be formed in amask. As shown in FIGS. 5F and 5G, standoff bumps 530 may be arranged ina pattern which may be evenly spaced as shown, unevenly spaced or may bein other arrangements such as hexagonally packed. Surrounding the bumps530 are another layer of dielectric material 540, and actuation metals540 are electrically isolated from the standoff bumps 530. In someaspects, the standoff bumps 530 can be 50 nm to 1.0 μm in height and 0.1μm to 5 μm in diameter. The actuation metal thicknesses range from 0.1μm to 0.5 μm. The lateral gap between the edge of the bump and thepatterned edge of the surrounding actuator metal should be as large orlarger than the height of the standoff bump.

The present subject matter can be embodied in other forms withoutdeparture from the spirit and essential characteristics thereof. Theembodiments described therefore are to be considered in all respects asillustrative and not restrictive. Although the present subject matterhas been described in terms of certain preferred embodiments, otherembodiments that are apparent to those of ordinary skill in the art arealso within the scope of the present subject matter.

What is claimed is:
 1. A micro-electro-mechanical system (MEMS) variablecapacitor, comprising: a fixed capacitive electrode attached to asubstrate; a fixed actuation electrode attached to the substrate; amovable component positioned above the substrate and movable withrespect to the fixed capacitive electrode and the fixed actuationelectrode, the movable component comprising: a movable capacitiveelectrode positioned above the fixed capacitive electrode, wherein atleast a portion of the movable capacitive electrode is spaced apart fromthe fixed capacitive electrode by a first gap; and a movable actuationelectrode positioned above the fixed actuation electrode, wherein themovable actuation electrode is spaced apart from the fixed actuationelectrode by a second gap that is larger than the first gap; and atleast one standoff bump positioned between the fixed actuation electrodeand the movable actuation electrode for maintaining a desired distancebetween the movable actuation electrode and the fixed actuationelectrode.
 2. The micro-electro-mechanical system (MEMS) variablecapacitor of claim 1, wherein the movable capacitive electrodecomprises: one or more first capacitive portions spaced apart from thefixed capacitive electrode by the first gap; and one or more secondcapacitive portions spaced apart from the fixed capacitive electrode bya distance greater than the first gap.
 3. The micro-electro-mechanicalsystem (MEMS) variable capacitor of claim 2, wherein a size of each ofthe one or more first capacitive portions is substantially similar to asize of the at least one standoff bump.
 4. The micro-electro-mechanicalsystem (MEMS) variable capacitor of claim 1, wherein the at least onestandoff bump comprises one or more first standoff bumps having a firstdimension by which the one or more first standoff bumps extends betweenthe fixed actuation electrode and the movable actuation electrode, thefirst dimension being substantially equal to the difference between thedimensions of the first gap and the second gap.
 5. Themicro-electro-mechanical system (MEMS) variable capacitor of claim 4,wherein the at least one standoff bump comprises one or more secondstandoff bumps having a second dimension by which the one or more secondstandoff bumps extends between the fixed actuation electrode and themovable actuation electrode, the second dimension being greater than thefirst dimension of the one or more first standoff bumps.
 6. Themicro-electro-mechanical system (MEMS) variable capacitor of claim 5,wherein the one or more first standoff bumps are positioned relativelycloser to the fixed capacitive electrode than the one or more secondstandoff bumps.
 7. The micro-electro-mechanical system (MEMS) variablecapacitor of claim 1, wherein one or more of the at least one standoffbump is attached to the substrate at or near the fixed actuationelectrode.
 8. The micro-electro-mechanical system (MEMS) variablecapacitor of claim 1, wherein one or more of the at least one standoffbump is attached to the movable component at or near the movableactuation electrode.
 9. The micro-electro-mechanical system (MEMS)variable capacitor of claim 1 wherein a difference between thedimensions of the first gap and the second gap measured in microns isgreater than a value of a ratio between an actuation voltageV_(actuation) and a maximum electric field E_(max) generated between themovable actuation electrode and the fixed actuation electrode, whereinV_(actuation) is between 10 and 100V, and wherein E_(max) is between 100and 1000 V/μm.
 10. The micro-electro-mechanical system (MEMS) variablecapacitor of claim 1, wherein the difference between the dimensions ofthe first gap and the second gap is selected such that a self-actuationvoltage between the movable actuation electrode and the fixed actuationelectrode is above a predetermined threshold value.
 11. Themicro-electro-mechanical system (MEMS) variable capacitor of claim 10,wherein the difference between the dimensions of the first gap and thesecond gap is less than or equal to one quarter of the dimension of thesecond gap.
 12. The micro-electro-mechanical system (MEMS) variablecapacitor of claim 1, wherein the difference between the dimensions ofthe first gap and the second gap is between about 10 nm and 500 nm. 13.A micro-electro-mechanical system (MEMS) variable capacitor, comprising:a fixed capacitive electrode attached to a substrate; a first fixedactuation electrode and a second fixed actuation electrode attached tothe substrate on opposing sides of the fixed capacitive electrode; amovable component comprising a first end that is fixed with respect tothe substrate and a second end opposite the first end that is fixed withrespect to the substrate, a center portion of the movable componentbeing positioned above the substrate and movable with respect to thefixed capacitive electrode, the first fixed actuation electrode, and thesecond fixed actuation electrode, the movable component comprising: afirst movable actuation electrode positioned above the first fixedactuation electrode; a second movable actuation electrode positionedabove the second fixed actuation electrode; and a movable capacitiveelectrode positioned above the fixed capacitive electrode; and at leastone standoff bump positioned between the fixed actuation electrode andthe movable actuation electrode for preventing contact of the movableactuation electrode with the fixed actuation electrode; wherein at leasta portion of the movable capacitive electrode is spaced apart from thefixed capacitive electrode by a first gap; wherein the first movableactuation electrode and the second movable actuation electrode arespaced apart from the first fixed actuation electrode and the secondfixed actuation electrode, respectively, by a second gap that is largerthan the first gap; and wherein a first dimension by which one or moreof the at least one standoff bump extends between the fixed actuationelectrode and the movable actuation electrode is substantially equal tothe difference between the dimensions of the first gap and the secondgap.
 14. The micro-electro-mechanical system (MEMS) variable capacitorof claim 13, wherein the at least one standoff bump comprises one ormore additional standoff bumps having a second dimension by which theone or more additional standoff bumps extends between the fixedactuation electrode and the movable actuation electrode, the seconddimension being greater than the first dimension.
 15. Themicro-electro-mechanical system (MEMS) variable capacitor of claim 14,wherein the one or more of the at lest one standoff bump are positionedrelatively closer to the fixed capacitive electrode than the one or moreadditional standoff bumps.